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Statistical Analysis of Flare Lyman-α Time Series from SORCE/SOLSTICE

Presentation #304.02 in the session From Filaments to Flares.

Published onSep 18, 2023
Statistical Analysis of Flare Lyman-α Time Series from SORCE/SOLSTICE

H I Lyman-α (1216 Å) is the strongest emission line in the solar spectrum, but until recently, most instruments have not had the cadence, sensitivity, and duty cycle to capture rapid changes in Lyman-α emission associated with flares. Of the observations that exist, the data are predominantly spatially and spectrally integrated. In January 2021, a new dataset from the SOLSTICE instrument onboard SORCE was released that scans through the Lyman-α line profile with modest spectral resolution (0.35 Å) on flare timescales (one line scan takes ~1 min). Here, we present the analysis of 4 X- and 13 M-class flares that were observed between 2003-2012. The Lyman-α profile was divided into 5 bands: line core (λrest ± 1.5 Å), ‘near’ wings (λrest ± 2-4 Å), and ‘far’ wings (λrest ± 4-6 Å). While relatively low resolution, these measurements of the Lyα line will allow us to determine how the chromosphere responds to flare heating at this wavelength, where in the solar atmosphere the emission is emanating, and how these changes contribute to the solar irradiance. We found the line core had an average enhancement of 3%, while the wings had average enhancements of 8-10%. These enhancements generally occurred before the GOES soft X-ray (SXR) peak, indicating the line was impulsively heated. However, in a third of the events the Lyman-α emission peaked after the GOES SXR peak. The wings generally peaked before the line core. The line profile flare excess was dominated by line core emission. Thus, despite experiencing more enhancement, the wing emission may not contribute to broadband observations. These datasets can be used as constraints on radiative hydrodynamic models investigating flare heating mechanisms.

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